Codopants (Cu, Li, Cr) mediating distribution of magnetic Co ions in Co-doped ZnO

X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) were combined to study the effect of (Cr, Cu, Li) codopants on the distribution of magnetic Co atoms in Co-doped ZnO thin films. For the single-doping of Co in ZnO, there are two occupation sites of Co in ZnO: the substitutional sites for Zn and metallic Co clusters. After Cr doping, the metallic Co clusters vanish and all the Co atoms occupy the substitutional sites. On the contrary, Cu(Li)-codoping further increases the content of metallic Co clusters. In-depth analysis suggests that the distinct roles of Cr and Cu(Li) codopants for mediating the distribution of Co atoms in ZnO are intimately related to the occupation sites of codopants.